A two B-Z junction containing DNA resolves into an all right-handed double-helix

Natural and artificial oligonucleotides are capable of assuming many differ ent conformations and functions. Here we present results of an NMR restrain ed molecular modelling study on the conformational preferences of the modif ied decanucleotide d((m)C1G2(m)C3G4C5(L)G6(L)(m)C7G8(m)C9G10).d((m)C11G12(m )C13G14C15(L)G(L)16(m)C17G18(m)C19G20) which contains L deoxynucleotides in its centre, This chimeric DNA was expected to form a right-left-right-hand ed B-type double-helix (BB*B) at low salt concentration. Actually, it matur ed into a fully right-handed double helix with its central C(L)pG(L) core f orming a right-handed Z-DNA helix embedded in a B-DNA matrix (BZ*B), The in terplay between base-base and base-sugar stackings within the core and its immediately adjacent residues was found to be critical in ensuring the stab ilisation of the right-handed helix, The structure could serve as a model f or the design of antisense oligonucleotides resistant to nucleases and capa ble of hybridising to natural DNAs and RNAs.